let intervalID = setInterval(myCallback, 1000);

function myCallback() {
    console.log(Date.now());
   }
  
// function stopChange() {
//     clearInterval(intervalID);
//    }
document.getElementById("stop").addEventListener("click", stopChange); 

function startChange() {
    if (!intervalID) {
    intervalID = setInterval(changeColor, 1000);
    }
   }

function stopChange() {
    clearInterval(intervalID);
   }

   function changeColor() {
    if (document.body.style.backgroundColor !== "black") {
    document.body.style.backgroundColor = "black";
    document.body.style.color = "white";
    } else {
    document.body.style.backgroundColor = "white";
    document.body.style.color = "black";
    }
   }

document.getElementById("start").addEventListener("click", startChange);

function changeRandomColor() {
    const randomColor = Math.floor(Math.random() * 16777215).
   toString(16);
    document.body.style.backgroundColor = `#${randomColor}`;
   }

intervalID = setInterval(changeRandomColor, 1000);
   